Process for the preparation of vitreous material notably for jewellery

Abstract

Manufacturing process for a lead silicate based material habing a characteristic coloring ranging from orange-tinged yellow to blood red, having the following steps: a) preparing a bath or molten mass of lead silicate, produced by mixing lead oxide PbO and silica SiO 2 in such proportions that the ratio between the two constituents is 65% by weight of lead oxide and 35% by weight of silica, whereby the temperature of fusion is chosen in the region of 1000° and 1300° C.; b) introducing into the fusion bath obtained during the foregoing state, copper oxide and a reducing agent, whereby the quantity of this addition is such that the concentration by weight of the copper oxide in the final product is in the region of 6 to 8%, the temperature of the fusion bath being maintained between 1000° amd 1300° C.; c) maintaining the fusion bath at rest always at the same temperature approximately between 1000° C. and 1300° C. in order to eliminate bubbles; d) heat treating of the material obtained in this way at a temperature between approximately 500° and 800° C. during a period of time sufficient to form and grow cuprite microcrystals (Cu 2 O); and e) slowly cooling the mass obtained to an ambient temperature in order to prevent residual stresses forming therein.

We claim: 
     
       1. A process for the manufacture of vitreous material exhibiting a characteristic color ranging from orangish-yellow to ox blood-red, based on lead silicate, comprising: a) preparing a lead silicate melt, by mixing lead oxide and silica to obtain a mixture comprising 65% by weight of lead oxid and 35% by weight silica, based on the total weight of the melt, at a melting temperature between about 1000° C. to 1300° C.;   b) adding copper oxide and antimony into the melt of step (a), the quantity of the addition being sufficient to obtain a final product having a copper oxide content of about 6 to 8% by weight, and maintaining the temperature of the melt between about 1000° C. and 1300° C.;   c) maintaining the melt at rest at a temperature of about 1000° to 1300° C., so as to eliminate bubbles;   d) heat treating of material resulting from step (c) at a temperature of between about 500° C. and 800° C. for a time sufficient to produce formation and growth of microcrystals of cuprite; and   e) slow cooling of material resulting from step (d) to room temperature in order to avoid formation of residual stresses therein.   
     
     
       2. The process according to claim 1, wherein the melt of step (a) is prepared by mixing siliceous sand and red lead. 
     
     
       3. The process according to claim 1, wherein the melt of step (a) is prepared by adding a lead silicate sinter. 
     
     
       4. The process according to claim 1, wherein during step (a) additional components are added to modify the chemical, physical and mechanical properties of the vitreous material. 
     
     
       5. The process according to claim 4, wherein said additional components comprise a member selected from the group consisting of oxides of lithium, sodium, potassium, calcium, magnesium, barium, aluminum, and phosphorus, and mixtures thereof. 
     
     
       6. The process according to claim 1, wherein the maintaining at rest of step (c) is from about a few minutes to about half an hour. 
     
     
       7. The process according to claim 1, wherein the heat treating of step (d) is performed at a temperature and a residence time so as to obtain a desired size of the microcrystals of cuprite. 
     
     
       8. A material comprising a transparent and colorless vitreous matrix composed essentially of lead silicate glass comprising a large quantity of crystals of cuprite which make the material opaque and give it a color ranging from orangish-yellow to ox blood-red, the relative density of the material being between about 4.0 and 4.5, said material being produced by a process comprising: a) preparing a lead silicate melt, by mixing lead oxide and silica to obtain a mixture comprising 65% by weight of lead oxide and 35% by weight silica, based on the total weight of the melt, at a melting temperature between about 1000° C. and 1300° C.;   b) adding copper oxide and antimony into the melt of step (a), the quantity of the addition being sufficient to obtain a final product having an oxide content of about 6 to 8% by weight, and maintaining the temperature of the melt between about 1000° C. and 1300° C.;   c) maintaining the melt at rest at a temperature of about 1000° to 1300° C., so as to eliminate bubbles;   d) heat treating of material resulting from step (c) at a temperature of between about 500° C. and 800° C. for a time sufficient to produce formation and growth of microcrystals of cuprite; and   e) slow cooling of material resulting from step (d) to room temperature in order to avoid formation of residual stresses therein.   
     
     
       9. A material comprising a transparent and colorless vitreous matrix composed essentially of lead silicate glass comprising a large quantity of crystals of cuprite which make the material opaque and give it a color ranging from orangish-yellow to ox blood-red, the relative density of the material being between about 4.0 and 4.5, said material being produced by a process comprising: a) preparing a lead silicate melt, by mixing lead oxide and silica to obtain a mixture comprising 65% by weight of lead oxide and 35% by weight silica, based on the total weight of the melt, at a melting temperature between about 1000° C. and 1300° C.;   b) adding copper oxide and a reducing agent into the melt of step (a), the quantity of the addition being sufficient to obtain a final product having an oxide content of about 6 to 8% by weight, and maintaining the temperature of the melt between about 1000° C. and 1300° C.;   c) maintaining the melt at rest at a temperature of about 1000° C. to 1300° C., so as to eliminate bubbles;   d) heat treating of material resulting from step (c) at a temperature of between about 500° C. and 800° C. for a time sufficient to produce formation and growth of microcrystals of cuprite; and   e) slow cooling of material resulting from step (d) to room temperature in order to avoid formation of residual stresses therein; and   said material comprising the following composition as percentage by weight:   ______________________________________                                    
PbO      52%           SiO.sub.2                                          
                               28%                                        
Cu.sub.2 O                                                                
         6%            Sb.sub.2 O.sub.3                                   
                               1%                                         
K.sub.2 O                                                                 
         5%            Na.sub.2 O                                         
                               2.5%                                       
Al.sub.2 O.sub.3                                                          
         2%            CaO     3%                                         
P.sub.2 O.sub.5                                                           
         0.5%.                                                            
______________________________________                                    
       
     
     
       10. A material comprising a transparent and colorless vitreous matrix composed essentially of lead silicate glass comprising a large quantity of crystals of cuprite which make the material opaque and give it a color ranging from orangish-yellow to ox blood-red, the relative density of the material being between about 4.0 and 4.5, said material being produced by a process comprising: a) preparing a lead silicate melt, by mixing lead oxide and silica to obtain a mixture comprising 65% by weight of lead oxide and 35% by weight silica, based on the total weight of the melt, at a melting temperature between about 1000° C. and 1300° C.;   b) adding copper oxide and a reducing agent into the melt of step (a), the quantity of the addition being sufficient to obtain a final product having an oxide content of about 6 to 8% by weight, and maintaining the temperature of the melt between about 1000° C. and 1300° C.;   c) maintaining the melt at rest at a temperature of about 1000° C. to 1300° C., so as to eliminate bubbles;   d) heat treating of material resulting from step (c) at a temperature of between about 500° C. and 800° C. for a time sufficient to produce formation and growth of microcrystals of cuprite; and   e) slow cooling of material resulting from step (d) to room temperature in order to avoid formation of residual stresses therein; and   said orangish-yellow color is obtained due to the presence of small-sized cuprite crystals, while the ox blood-red color is obtained due to the presence of cuprite crystals of larger size.   
     
     
       11. The material according to claim 10, wherein the size of said cuprite crystals varies between about 2 microns and 2 mm. 
     
     
       12. A jewelry material comprising a transparent and colorless vitreous matrix composed essentially of lead silicate glass comprising a large quantity of crystals of cuprite which make the material opaque and give it a color ranging from orangish-yellow to ox blood-red, the relative density of the material being between about 4.0 and 4.5. 
     
     
       13. The jewelry material according to claim 12, comprising the following composition as percentage by weight:   ______________________________________                                    
PbO      52%           SiO.sub.2                                          
                               28%                                        
Cu.sub.2 O                                                                
         6%            Sb.sub.2 O.sub.3                                   
                               1%                                         
K.sub.2 O                                                                 
         5%            Na.sub.2 O                                         
                               2.5%                                       
Al.sub.2 O.sub.3                                                          
         2%            CaO     3%                                         
P.sub.2 O.sub.5                                                           
         0.5%.                                                            
______________________________________                                    
     
     
     
       14. The jewelry material according to claim 12, wherein the orangish-yellow color is obtained due to the presence of small-sized cuprite crystals, while the ox blood-red color is obtained due to the presence of cuprite crystals of larger size. 
     
     
       15. The jewelry material according to claim 14, wherein the size of said cuprite crystals varies between about 2 microns, and 2 mm. 
     
     
       16. A jewelry material produced by the process of claim 1.